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Spectrochimica Acta Part A 86 (2012) 375– 380

Contents lists available at SciVerse ScienceDirect

Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

j ourna l ho me page: www.elsev ier .com/ locate /saa

pectrofluorimetric study of the interaction between europium(III) andoxifloxacin in micellar solution and its analytical application

ohammad Kamruzzamana,d, Al-Mahmnur Alama, Sang Hak Leea,d,∗, Dhanusuraman Ragupathya,oung Ho Kimb,∗∗, Sang-Ryoul Parkc, Sung Hong Kimd

Department of Chemistry, Kyungpook National University, Daegu 702-701, South KoreaResearch Institute of Advanced Energy Technology, Kyungpook National University, Daegu 702-701, South KoreaCenter for Bioanalysis, Korea Research Institute of Standards and Science, Daejeon 305-401, South KoreaKorea Basic Science Institute Daegu Center, Daegu 702-701, South Korea

r t i c l e i n f o

rticle history:eceived 16 March 2011eceived in revised form 7 September 2011ccepted 23 October 2011

eywords:pectrofluorimetry

a b s t r a c t

A sensitive spectrofluorimetric method has been developed for the determination of moxifloxacin (MOX)using europium(III)–MOX complex as a fluorescence probe in the presence of an anionic surfactant,sodium dodecyl benzene sulfonate (SDBS). The fluorescence (FL) intensity of Eu3+ was enhanced by com-plexation with MOX at 614 nm after excitation at 373 nm. The FL intensity of the Eu3+–MOX complexwas significantly intensified in the presence of SDBS. Under the optimum conditions, it was found thatthe enhanced FL intensity of the system showed a good linear relationship with the concentration of

−11 −9 −1

uropium(III)oxifloxacin

odium dodecyl benzene sulfonate

MOX over the range of 1.8 × 10 –7.3 × 10 g mL with a correlation coefficient of 0.9998. The limit ofdetection of MOX was found to be 2.8 × 10−12 g mL−1 with relative standard deviation (RSD) of 1.25% for5 replicate determination of 1.5 × 10−8 g mL−1 MOX. The proposed method is simple, offers higher sensi-tivity with wide linear range and can be successfully applied to determine MOX in pharmaceutical andbiological samples with good reproducibility. The luminescence mechanism is also discussed in detailwith ultraviolet absorption spectra.

. Introduction

Moxifloxacin (MOX) (1S,6S)-1-cyclopropyl-7-[2,8-iazobicyclo(4.3.0)non-8-yl]-6-fluoro-8-methoxy-4-oxo-1,4-ihydroquinolone-3-carboxylic acid, is a fourth generation new-methoxyquinolone derivate of fluoroquinolones with enhancedctivity in vitro against Gram positive bacteria and maintenancef activity against Gram negative bacteria [1–3]. The bactericidalctivity of MOX is mediated by the inhibition of DNA gyrasetopoisomerase II) and topoisomerase IV, essential enzymesnvolved in bacterial DNA replication, transcription, repair andecombination [4]. MOX is prescribed for the bacterial infectionsf the respiratory tract including sinusitis, community acquiredneumonia and acute exacerbations of chronic bronchitis [5]. Therug is rapidly absorbed, reaching maximum plasma concentra-

ions between 1 and 4 h after oral administration; its half-life of1–15 h allows a daily administration [3]. MOX is administered toatients in 400 mg daily doses, being that the final concentrations

∗ Corresponding author at: Department of Chemistry, Kyungpook National Uni-ersity, Daegu 702-701, South Korea. Tel.: +82 53 950 5338; fax: +82 53 950 6330.∗∗ Corresponding author. Tel.: +82 53 950 7869; fax: +82 53 950 7879.

E-mail addresses: shlee@knu.ac.kr (S.H. Lee), youngkim@knu.ac.kr (Y.H. Kim).

386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.saa.2011.10.051

© 2011 Elsevier B.V. All rights reserved.

in serum and urine for the treated patients are of 2.00–5.00and 30.00–60.00 �g mL−1, respectively [6]. Bayer AG developedthe drug and it is marketed worldwide (as the hydrochloride)under the brand name Avelox for oral treatment. It achieves goodtissue penetration and has a convenient once-daily administrationschedule, as well as being available in both intravenous and oralformulations in some markets. Due to clinical advantages of MOX,it is still meaningful to develop a simple and sensitive analyticalmethod for the determination of MOX.

Several methods have been reported for the quantification ofMOX including spectrofluorimetry [7], voltametry [8], squere-waveadsorptive voltammetry [9], square-wave voltammetry using Cu(II)[10], high-performance liquid chromatography (HPLC) with fluo-rescence [11–13], HPLC with UV detection [14], high-performancethin layer chromatography (HPTLC) [15], capillary electrophoresiswith laser-induced fluorescence [16], liquid chromatography [2]and chemiluminescence coupled with flow-injection (CL-FIA) [17].However, most of these methods are lacking in sensitivity, selec-tivity or require sophisticated instruments. Spectrofluorimetry is asimple and highly sensitive method for the assay of a large num-

ber of drugs and metals and permits the selective and sensitivedetermination of low concentrations of an analyte.

Europium complex has been used widely as a fluorescenceprobe for the determination of some biomolecules including,

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atX

76 M. Kamruzzaman et al. / Spectroc

etacycline-europium to determine lysozyme [18], Eu3+-oxycycline complex to determine NADP [19], tetracycline-Eu3+

o determine bilirubin [20], europium-thenoyltrifluoroacetonend doxycycline–europium to determine human serum albumin21,22], and oxytetracycline–Eu3+ to determine nucleic acid [23].uropium complex has been used as fluorescence probe becausef its high fluorescence quantum yield, large Strokes’ shift, narrowmission bands, and a long fluorescence lifetime and hence tovoid potential background fluorescent emission interferencesrom the biological matrix [24]. There was no report about spec-rofluorimetric method for the determination of MOX using Eu3+

s fluorescence probe. MOX having carboxylic and keto-oxygentoms are involved in complexation with Eu3+ which shows a largetokes’ shift and narrow emission bands.

In the present paper, a fluorescence system, Eu3+–MOX–sodiumodecyl benzene sulfonate (SDBS) has been proposed. In our study,he experimental results indicate that MOX could form a complexith Eu3+ and emit characteristic fluorescence of Eu3+ at 591 and

14 nm corresponding to the 5D0–7F1 and 5D0–7F2 transition ofu3+ ion respectively. It was also observed that the fluorescencentensity of Eu3+–MOX was enhanced significantly in the presencef SDBS and the enhanced intensity was proportional to the con-entration of MOX added. Therefore, a sensitive method for theetermination of MOX based on the fluorescence enhancementffect by the Eu3+–MOX complex in the presence of SDBS wasroposed. The characteristics of the fluorescence spectrum of theu3+–MOX–SDBS system and the effect of different experimentalonditions on the fluorescence intensity were studied systemat-cally. The proposed method is easily carried out, affords goodrecision and accuracy and has been successfully applied to theetermination of MOX in pharmaceutical preparations and biolog-

cal fluids with satisfactory results which signifies the importancef this work.

. Materials and methods

.1. Reagents

All chemicals were of analytical reagent grade and were usedithout further purification. Distilled deionised (DI) water (Mill-ore, MilliQ Water System, USA) was used throughout. MOX wasurchased from Sigma–Aldrich (St. Louis, USA). A stock solution1.0 × 10−3 mol L−1) of MOX was prepared in DI water. Work-ng solutions of desired concentrations were freshly prepared byppropriate dilution of each stock solution with DI water. Stocktandard solution of Eu3+ (1.0 × 10−3 mol L−1) was prepared byissolving Eu2O3 (purity, 99.99%) in 1:1 HCl and evaporating theolution to almost dryness before diluting to 100 mL with DIater. The stock standard solution was kept in the refrigerator

t 4 ◦C. The working standard solutions were prepared by appro-riate dilution with water. Sodium dodecyl benzene sulfonateSDBS) (1 × 10−3 mol L−1) was prepared by dissolving 0.017 g in

50 mL volumetric flask using DI water and preserved at 4 ◦C.ris–HCl buffer was prepared by dissolving appropriate amount ofris(hydroxy methyl) aminomethane in 500 mL DI water and pHas adjusted using 0.1 M HCl. Working solutions were preparedaily from the stock solution by appropriate dilution immediatelyefore used.

.2. Apparatus

All the spectrofluorimetric measurements were conducted with spectrofluorimeter (Model F-4500, Hitachi, Japan). The spec-rofluorimeter was equipped with a 450-W Xenon lamp (ModelBO 450 W/1, Osram, Germany) as the excitation light source and

a Acta Part A 86 (2012) 375– 380

a photomultiplier tube (Model R928, Hamamatsu, Japan) poweredat 950 V as the detector. The excitation and emission slits were set to10 nm to measure all fluorescence spectra. pH was adjusted usinga pH meter (Model Orion, 520A, USA). All the UV–visible spectrawere measured in UV-1800 (Shimadzu, Japan).

2.3. Analytical procedure

Apparent fluorescence (FL) excitation and emission spectrawere measured at room temperature and optimum excitation andemission wavelengths were found from these spectra. To a 10 mLvolumetric flask, solutions were added in the following order: 1 mLof Eu3+ ion solution, 1 mL of buffer solution, certain amount of MOX,and 1 mL of SDBS. The mixture was diluted to 10 mL with doubly DIwater, mixed thoroughly, and stood for 20 min. The solution wasthen put into the 1 cm quartz cell for measuring FL spectra andintensities. The FL intensity was measured with a 1 cm quartz cellwith an excitation wavelength of 373 nm and an emission wave-length of 614 nm.

2.4. Sample preparation

Commercially available 10 tablets of Avolex (each contains400 mg MOX) were weighed and grounded to fine powder by pestlein a mortar. The powder was transferred into a 1 L calibrated darkflasks containing 500 mL of DI water and dissolved in ultrasonicbath for 20 min and diluted to the mark with DI water. The dissolvedsample was filtered through a Millipore membrane filter paper anddiluted with DI water to obtain the appropriate concentration foranalysis of MOX.

The proposed procedure was applied to determine MOX inspiked human urine and serum samples. Urine and serum sam-ples were spiked with appropriate amounts of MOX stock solution.The serum sample was deproteinized by adding 5 mL of 20%trichloroacetic acid (CCl3COOH) in a centrifuge tube and cen-trifuged for 15 min at 8000 rpm. 0.1 mL of the prepared serumsample was mixed with the standard solutions of MOX and dilutedappropriately within the linear range of determination. For theurine samples, further pretreatment was not required exceptproper dilution in order to make the concentrations of MOX withinthe working range.

3. Results and discussion

3.1. Spectral characteristics of fluorescence

The FL emission and excitation spectra of (1) Eu3+; (2) MOX;(3) Eu3+–MOX; (4) Eu3+–MOX–SDBS are shown in Fig. 1. It can beobserved from Fig. 1 that only Eu3+ ion solution exhibited weak flu-orescence signal because of weak absorption of the metal ion itself(Fig. 1a, curve 1). When MOX was added into the Eu3+ ion solution,the characteristic FL peaks appeared at 591 and 614 nm (Fig. 1a,curve 3) corresponding to the 5D0–7F1 and 5D0–7F2 transition ofEu3+, respectively and maximum emission peak was obtained at614 nm. It is reported that luminescence intensities of the 5D0–7F1and 5D0–7F2 emissions are very sensitive to the nature of the lig-and environment. But the 5D0–7F1 transition retains its magneticdipole character in low symmetry systems, and its radiative tran-sition probability is not much affected by the ligand environment.On the other hand, the 5D0–7F2 is predominantly associated withelectric dipole, and their radiative transition probabilities are verysensitive to the nature of the ligand environment [25]. Thus, the

FL intensity was enhanced significantly at 614 nm after the addi-tion of MOX (Fig. 1a, curve 3). The results indicated that MOX canform a binary complex with Eu3+ which can emit the characteristicfluorescence of Eu3+. It is hypothesized that MOX can absorb the

M. Kamruzzaman et al. / Spectrochimica Acta Part A 86 (2012) 375– 380 377

450 500 55 0 60 0 6500

500

1000

1500

2000

2500FL

Inte

nsity

(a.u

.)

Wavelength (nm)

1

2 3

4a

b

300 350 40 0 45 00

500

1000

1500

2000

2500

3000

3500

FL In

tens

ity (a

.u.)

Wavelength (nm)

1

2

3

4

Fig. 1. Fluorescence emission (a) and excitation (b) spectra of Eu3+–MOX–SDBSs 3+ 3+ 3+

M0

lteiatgSMw

E3ie

3

ETFw

7.5 8.0 8.5 9. 0 9.5 10 .0 10.50

500

1000

1500

2000

2500

FL In

tens

ity (a

.u.)

pH

3.4. Effect of surfactant

Surfactants can solubilize hydrophobic compounds and improvethe microenvironment of luminescence which has frequently been

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00

500

1000

1500

2000

2500

10-5 [E u3+ ] ( mo l L-1 )

FL In

tens

ity (a

.u.)

ystem. (1) Eu ; (2) MOX; (3) Eu –MOX; (4) Eu –MOX–SDBS. Conditions:OX, 5.0 × 10−9 g mL−1; Eu3+, 1.7 × 10−5 mol L−1; SDBS, 7.0 × 10−4 mol L−1; Tris–HCl,

.01 mol L−1; pH, 9.2.

ight energy and transfer it to Eu3+ through intramolecular energyransfer. The FL intensity of the Eu3+–MOX complex at 614 nm wasnhanced markedly after the addition of SDBS (Fig. 1a, curve 4) bymproving the coordination microenvironment of Eu3+ and MOXnd decreased the combination between the water molecules andhe binary complex. As a result, the FL intensity of the system wasreatly enhanced which indicated that the existence of Eu3+ andDBS had a synergistic enhancement effect on the FL intensity ofOX. These may be due to Eu3+ and SDBS being able to coordinateith MOX, resulting in a very stable ternary complex.

From the excitation spectra (Fig. 1b), it could be seen thatu3+–MOX–SDBS system showed two excitation peaks at 310 and73 nm. Considering the interference of multiple peak and max-

mum emission intensity, 373 nm and 614 nm were chosen asxcitation and emission wavelengths respectively for this study.

.2. Effect of pH and buffers

The relationship between the FL intensity of the3+

u –MOX–SDBS system and the pH value is shown in Fig. 2.

he pH value was varied in the range of 8–10 and the maximumL intensity was obtained at 9.2. Thus, an optimal pH of 9.2as selected for the present study. The effects of the following

Fig. 2. Effect of pH on the FL intensity of Eu3+–MOX–SDBS system. Conditions:MOX, 5.0 × 10−9 g mL−1; Eu3+, 1.7 × 10−5 mol L−1; SDBS, 7.0 × 10−4 mol L−1; Tris–HCl,0.01 mol L−1.

buffer solutions on the FL intensity were also investigated;KH2PO4–Na2HPO4, borax–HCl, NH4Cl–NH3, NH4Cl–NH3·H2O,KH2PO4–NaOH, and Tris–HCl. Among the above buffers, Tris–HCloffers the highest sensitivity at a concentration of 0.01 mol L−1.Therefore, 0.01 mol L−1 Tris–HCl of pH 9.2 was chosen for thisstudy.

3.3. Effect of Eu3+ concentration

The influence of the concentration of Eu3+ on the FL intensitywas investigated in the range of 2 × 10−6–3.5 × 10−5 mol L−1. TheFL intensity was increased with the increase of the concentration ofEu3+ up to 1.7 × 10−5 mol L−1 (Fig. 3). Therefore, 1.7 × 10−5 mol L−1

was selected as optimal Eu3+ concentration to obtain the maximumFL intensity.

Fig. 3. Effect of Eu3+ concentration on the FL intensity of Eu3+–MOX–SDBSsystem. Conditions: MOX, 5.0 × 10−9 g mL−1; SDBS, 7.0 × 10−4 mol L−1; Tris–HCl,0.01 mol L−1; pH, 9.2.

378 M. Kamruzzaman et al. / Spectrochimica Acta Part A 86 (2012) 375– 380

0.2 0.4 0.6 0.8 1.0 1.20

500

1000

1500

2000

2500FL

Inte

nsity

(a.u

.)

10-3 [S DBS] ( mol L-1 )

FCp

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3

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3

acbosestsid

3

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Table 1Tolerance limit of foreign substances on the determination of MOX.

Foreign substance Maximumtolerableconcentration ratio

Change inflourescenceintensity (%)

Na+, K+ 2000 +1.22Al3+, Ca2+, Mg2+ 1500 −2.5Starch, fructose, glucose 300 −1.25Sucrose, dextrin, lactose, galactose 100 +1.03Penicillin 50 +2.3Sulbactum 40 −3.1

might interact with Eu . Moreover, the coordination numberof Eu3+ (usually 6–10) could not satisfied after the Eu3+–MOXcomplex formation, and Eu3+, therefore could interact with SDBSby electrostatic attraction which could bind tightly with the

210 245 280 315 35 0 385 4200.0

0.3

0.6

0.9

1.2

1.5

1.8

FL In

tens

ity (a

.u.)

1

2

3

4

5

6

ig. 4. Effect of SDBS concentration on the FL intensity of Eu3+–MOX–SDBS system.onditions: MOX, 5.0 × 10−9 g mL−1; Eu3+, 1.7 × 10−5 mol L−1; Tris–HCl, 0.01 mol L−1;H, 9.2.

mployed to increase the fluorescence intensities of weakly flu-rescent compounds [26,27]. The experiments indicated that theurfactants had a great effect on the fluorescence intensity of theystem. Thus, the FL intensity of the Eu3+–MOX system was mea-ured in the presence of different kinds of surfactant including,etyl trimethyl ammonium bromide (CTAB), Triton X-100, sodiumodecyl sulfate (SDS), and SDBS. The results showed that the mostffective surfactant was SDBS to enhance the FL intensity signif-cantly. The effect of SDBS concentration on the FL intensity wasxamined over the range of 2 × 10−4–1.2 × 10−3 mol L−1. The FLntensity was increased with increasing the concentration of SDBSn the range of 2 × 10−4–7 × 10−4 mol L−1 (Fig. 4), then started toecrease. Thus, the SDBS concentration of 7 × 10−4 mol L−1 washosen for the present study.

.5. Effect of the addition order of reagents

The effect of the order of addition of reagents on the FL intensityas studied and the results indicated that the following addi-

ion order; Eu3+, MOX, Tris–HCl, SDBS showed the maximum FLntensity. Therefore, this addition order was chosen for the wholexperiment. The experiments also showed that the FL intensity ofhe system reached a maximum in 20 min after all the reagents hadeen added and remained stable for at least 2 h.

.6. Interference study

In order to investigate the selectivity of the proposed method, systematic study of various interferents on the FL intensity werearried out. The interferents can affect the analytical performancey suppressing or enhancing the FL intensity. Thus, the effectf potential interferents was investigated by preparing a set ofolutions, each one with 3.5 × 10−8 mol L−1 of MOX and differ-nt concentrations of the chemical species to be tested. A foreignpecies is considered to interfere if it produces an error greaterhan ±5% in the determination of MOX. The results obtained areummarized in Table 1. The results indicated that no significantnterference could be observed for the foreign substances in theetermination of MOX.

.7. Linear range and detection limit

Under the optimum conditions, calibration graphs for the deter-ination of MOX by plotting the concentration of MOX versus FL

Aspirin 30 +2.45Paracetamol 20 +1.55

intensities were constructed. The enhanced fluorescence intensityof the system showed a good linear relationship within the MOXconcentration over the range of 1.8 × 10−11–7.3 × 10−9 g mL−1.The regression equation was Y = 2.31 × 1011CMOX + 395 (r = 0.9998)where CMOX is the concentration of MOX and Y is the fluorescenceintensity in arbitrary unit (a.u.). The limit of detection (LOD) asdefined by IUPAC, CLOD = 3Sb/m (where Sb is the standard deviationof the blank signals and m is the slope of the calibration graph)was found to be 2.8 × 10−12 g mL−1 for MOX. The relative stan-dard deviation (RSD) was 1.25% for 5 replicate determination of1.5 × 10−8 g mL−1 MOX.

3.8. Luminescence mechanism

MOX is a lower polar and hydrophobic compound, and its sol-ubility can be improved in the micellar solution. When Eu3+–MOXcomplex was isolated and congregated together with the micelles,the microenvironment of the complex was greatly amended, whichcould reduce the non-radiative energy loss through molecule col-lisions and improve the quantum efficiency of fluorescence [28].Thus, the presence of Eu3+ and SDBS had a synergistic effect toenhance the fluorescence intensity of Eu3+.

The ultraviolet absorption spectra were recorded to understandthe interaction of Eu3+, MOX and SDBS and shown in Fig. 5. It canbe observed that the absorption of SDBS (Fig. 5, curve 2) increasedwhen Eu3+ was added (Fig. 5, curve 3) which signified that SDBS

3+

Waveleng th (n m)

Fig. 5. Ultraviolet absorption spectra. (1) Eu3+; (2) SDBS; (3) Eu3+–SDBS; (4) MOX;(5) Eu3+–MOX; (6) Eu3+–MOX–SDBS. Conditions: MOX, 1.5 × 10−8 g mL−1; Eu3+,2.5 × 10−5 mol L−1; SDBS, 6 × 10−4 mol L−1; Tris–HCl, 0.01 mol L−1; pH, 9.2.

M. Kamruzzaman et al. / Spectrochimica Acta Part A 86 (2012) 375– 380 379

Table 2Results of determination of MOX in pharmaceutical preparations.

Sample (tablet) Amount (mg) Added (×10−8 mol L−1) Found (×10−8 mol L−1) ± RSDa Recovery (%)

Labled (mg) Found by the proposed method ± RSDa

Avolex 400 mg of MOX 398.7 ± 0.75

1.00 1.02 ± 1.25 1022.00 1.94 ± 1.05 973.00 3.11 ± 1.65 103.674.00 3.96 ± 0.85 995.00 5.09 ± 1.35 101.8

a Relative standard deviation for three replicate measurements.

Table 3Recovery of MOX in serum and urine samples.

Standard addition method

Samples Serum Urine

Added (×10−8 mol L−1) Observed(×10−8 mol L−1) ±RSDa (%)

Recovery (%) Added (×10−8 mol L−1) Observed(×10−8 mol L−1) ±RSDa (%)

Recovery (%)

2.0 2.08 ± 0.9 104 2.0 1.93 ± 1.45 96.5.25

.5

EFpttewitiMSosb5Ecawta(oi

4

4

mrdttmM

4

t

Moxifloxacin 4.0 3.97 ± 1.5 996.0 6.03 ± 1.22 100

a Relative standard deviation for three replicate measurements.

u3+–MOX complex and perform a good protection function. Fromig. 5 (curve 4), it was observed that MOX showed two absorptioneaks at 289 and 339 nm. When Eu3+ was added to the MOX solu-ion, a red shift occurs at longer wavelength from 289 and 338 nmo 307 and 369 nm (Fig. 5, curves 4 and 5) and the absorbency wasnhanced which indicated that MOX can form a binary complexith Eu3+ by absorbing light energy and transfer it to Eu3+ through

ntramolecular energy transfer. The spectral shift may be due tohe formation of binary complex between MOX and Eu3+ throughntramolecular energy transfer [20,29]. However, the absorption of

OX was enhanced significantly with the addition of both Eu3+ andDBS which was in accordance with the fluorescence incrementf the fluorescence excitation spectrum of the Eu3+–MOX–SDBSystem (Fig. 1b) and the absorption wavelength showed a slightlue shift from 307 and 369 nm to 304 and 364 nm (Fig. 5, curves

and 6). Moreover, a multiple ionic associate was formed in theu3+–MOX–SDBS system which increased the effective absorptionross-section of the complex resulting in the increase of molarbsorbance index. Thus, the fluorescence intensity of the systemas significantly increased with the addition of SDBS. In addition,

he optimum concentration of SDBS in the presented study waspproximated to the critical micelle concentration (CMC) of SDBSCMC = 0.63 mmol L−1) [30], which indicated that the formationf micelle had great effect on the enhancement of fluorescencentensity of the system.

. Application

.1. Determination of MOX in pharmaceutical preparations

The proposed method was applied to determine MOX in com-ercially available pharmaceutical preparations, Avolex and the

esults obtained are listed in Table 2. There were no significantifferences between the labeled contents and those obtained byhe proposed method. Recovery studies were also performed onhe Avolex tablets (containing 400 mg MOX) by standard addition

ethod. Recoveries were observed in the range of 97–103.67% forOX.

.2. Determination of MOX in spiked serum and urine samples

The proposed method was used to determine the MOX con-ent of serum and urine samples. In order to adjust the sample

4.0 4.11 ± 0.91 102.756.0 6.07 ± 1.35 99.5

concentration of MOX within the linear range of determination,the supernatant of the centrifuged serum and urine samples wasused to investigate the recovery by standard addition method. Theresults are shown in Table 3. Recoveries of MOX contents in serumand urine samples were 99.25–104% and 96.5–102.75% respec-tively. Therefore, the proposed method can be applied to determineMOX in serum and urine samples with good accuracy.

5. Conclusion

A sensitive, simple and responsive spectrofluorimetric methodhas been proposed based on the sensitization of the characteris-tic FL intensity of Eu3+ by SDBS which can be applied successfullyfor the determination of MOX in human urine and serum sam-ples and formulated pharmaceutical products. The FL intensityof the Eu3+–MOX system was enhanced markedly by incorpo-rating SDBS allowing the rapid determination of MOX with verylow limit of detection (2.8 × 10−12 g mL−1), good reproducibilityand wide dynamic range (1.8 × 10−11–7.3 × 10−9 g mL−1). Recov-ery study also performed under standard addition method andhas been applied to the determination of MOX in pharmaceuticalpreparations and biological samples with satisfactory result.

Acknowledgements

This work was supported by the Korea Research Council of Fun-damental Science and Technology (KRCF) through Basic ResearchProject managed by the Korea Research Institute of Standards andScience (KRISS). This work was supported by the Priority ResearchCenters Program through the National Research Foundation ofKorea (NRF) funded by the Ministry of Education, Science and Tech-nology (2009-0093819).

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